The present invention relates to an engine idling speed control sysgem for a vehicle, and more particularly to a system which is provided with a device for preventing the running on of the engine operation after turning off of the ignition switch of the engine.
Heretofore, a closed loop feedback control system has been provided for controlling the idling speed to a desired idling speed by adjusting the amount of air or the amount of the air-fuel mixture to be induced in the engine in dependency on an error signal which is the difference between a desired reference idling speed and the detected idling speed.
On the other hand, it occasionally happens that the engine runs on even if the ignition switch is turned off. In order to prevent the running on of the engine operation, there has been proposed a system using an actuator in the above described automatic idling speed control system. The actuator comprises a motor and an axially movable rod driven by the motor. In the proposed system, a throttle valve follows the retraction of the rod of the actuator to close the induction passage of the engine. When the ignition switch is turned off, the rod of the actuator is further retracted, so that the throttle valve, rotates from the idling open position to a further closed position to stop the engine running.
In such a system, the rod of the actuator moves a considerablly long distance, that is the actuator must be operated over a wide range. After the throttle valve has reached the closed position, the rod of the actuator is further retracted to a predetermined position.
It is disadvantageous that the actuator has a wide operational range for the maintenance of the actuator, because such a wide range operation is more apt to cause breakdown of the actuator.